The IJW120R100T1 is a depletion mode / normally-on device, like the SJDP120R085. The caveat is that the threshold voltage is much 'higher' at -12V to -15V as opposed to -4V to -6V in the SJDP120R085, which makes (self)biasing more difficult still.

The SJEP120R100A is an enhancement mode/normally off and needs the gate to be biased positively at 0.75V to 1.5V to turn the device on.